Effects of polyamines on higher-order folding of in situ chromatin

Modifications of the higher-order chromatin structure induced by polyamines have been quantitatively investigated in situ through a non-invasive bioph ysical approach using Differential Scanning Calorimetry and Quantitative Fl uorescence Microscopy. Calorimetric and intensitometric profiles have been acquired for samples of native thymocytes, alternatively suspended in buffe rs, with or without natural polyamines (spermine and spermidine). The resul ts here reported show that the structure and distribution of nuclear chroma tin in situ considerably change upon the ionic composition of the environme nt. A quantitative analysis of this data and a comparison with previous res ults obtained from isolated chromatin fibers was carried out. Finally, an i nverse relationship between chromatin condensation and nuclear volume was o bserved.